1608. Special Array With X Elements Greater Than or Equal X

Easy

You are given an array nums of non-negative integers. nums is considered special if there exists a number x such that there are exactly x numbers in nums that are greater than or equal to x.

Notice that x does not have to be an element in nums.

Return x if the array is special, otherwise, return -1. It can be proven that if nums is special, the value for x is unique.

Example 1:

Input: nums = [3,5]
Output: 2
Explanation: There are 2 values (3 and 5) that are greater than or equal to 2.

Example 2:

Input: nums = [0,0]
Output: -1
Explanation: No numbers fit the criteria for x.

  If x = 0, there should be 0 numbers >= x, but there are 2.
  If x = 1, there should be 1 number >= x, but there are 0.
  If x = 2, there should be 2 numbers >= x, but there are 0.
  x cannot be greater since there are only 2 numbers in nums.

Example 3:

Input: nums = [0,4,3,0,4]
Output: 3
Explanation: There are 3 values that are greater than or equal to 3.

Constraints:

1 <= nums.length <= 100
0 <= nums[i] <= 1000

Solution:

class Solution {

    /**
     * @param Integer[] $nums
     * @return Integer
     */
    function specialArray($nums) {
        sort($nums);

        if ($nums[0] >= count($nums))
            return count($nums);

        for ($i = 1; $i < count($nums); ++$i) {
            $count = count($nums) - $i;
            if ($nums[$i - 1] < $count && $nums[$i] >= $count)
                return $count;
        }

        return -1;
    }
}

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